Performance Analysis of Brushless Wound Rotor Vernier Machine by Utilizing Third Harmonic Field Excitation

In this paper, a self-excited topology by utilizing third harmonic field excitation is proposed for realizing the brushless operation of the Wound Rotor Vernier Machine (WRVM). The proposed topology consists of two windings housed inside the stator periphery connected in series with the three-phase diode rectifier. The two windings on the stator periphery are the 12-pole excitation and 4-pole armature winding. The 12-pole excitation winding is linked to the open-end star winding of 4-pole armature winding with the help of a three-phase diode rectifier. When the current is supplied by the inverter, a 4-pole, and a 12-pole Magneto Motive Force (MMF) is developed in the machine air gap. The 4-pole fundamental MMF component develops the main stator field and a 12-pole MMF component develops the third harmonic field. The third harmonic field tends to induce a harmonic current in the harmonic winding which is housed inside the rotor periphery. The induced harmonic current is then rectified by the means of an H-bridge rectifier to excite the rotor field winding, and this realizes the brushless operation of a WRVM. The Two-dimensional Finite Element Analysis (2D-FEA) is carried out in a JMAG designer software to validate the operation of the proposed BL-WRVM. Furthermore, the proposed topology is analyzed for the comparative analysis with the sub-harmonic model after the verification of FEA results. The comparative analysis shows that the third harmonic topology results in improved average torque when compared to the subharmonic wound-rotor vernier machine.